Two conservation groups sued the federal government Tuesday claiming marine mammal regulators are not doing enough to protect polar bears and walruses against the combined threat of oil and gas exploration and global warming.

The groups say the U.S. Fish and Wildlife Service did not fully consider the effects of global warming, such as diminished sea ice, as it wrote regulations allowing for incidental harassment of polar bears and walruses by the industry in the Beaufort Sea and nearby coastal areas.

Polar bears depend on sea ice for their main prey, ringed seals and bearded seals. Beaufort Sea females use coastal land or sea ice for digging snow caves to give birth.

Female walruses follow the receding ice edge north in spring and summer, using the ice as a platform to dive to the bottom and feed while calves remain on the ice.

Polar bears can suffer harm from drilling, seismic work and transportation, said Earthjustice attorney Clayton Jernigan, who filed the lawsuit on behalf of the Center for Biological Diversity and Pacific Environment, both based in California. The petroleum activities disturb feeding, cause abandonment of maternity dens and disrupt polar bear life cycles, Jernigan said.

Officials for the Fish and Wildlife Service in Anchorage had not seen the lawsuit and had no immediate reaction. Offices in Washington, D.C., closed early Tuesday because of an ice storm.

The lawsuit focuses on the legal "incidental taking" of polar bears and walrus, a broad definition that covers killing plus harassment that disturbs a behavior. It could mean driving a truck near a polar bear den and causing the bear to come out to investigate, said Kassie Siegel of the Center for Biological Diversity.

"That's take, even if you don't then run over the bear and kill her," Siegel said.

Siegel was lead author of the center's petition that forced the federal government to consider whether to list polar bears as threatened under the Endangered Species Act due to global warming. Public comment is open until April 9 and a decision is due at the end of the year.

The Marine Mammal Protection Act, passed in 1981, imposes a general moratorium on the taking of marine mammals. Congress created limited exceptions for occurrences incidental to a specific activity such as drilling for oil and gas.

The Fish and Wildlife Service is authorized to issue regulations for five-year periods for such incidental activity, with the latest issued in August. By law, the total effect on the population must be negligible.

The lawsuit claims the agency did not assess the added stress of warming in the Arctic before issuing the regulations.

"The government is well aware that global warming threatens polar bears with extinction and is transforming the entire Arctic ecosystem, yet these regulations fail to take this into account," Siegel said.

The lawsuit cites a federal study released in November that showed fewer polar bear cubs are surviving off Alaska's northern coast. The study of bears in the south Beaufort Sea, which spans the northern coasts of Alaska and western Canada, also found that adult males weigh less and have smaller skulls than those captured and measured two decades ago.

Other studies indicate global warming and diminished sea ice may be linked to drowning, starvation and cannibalism among the bears, said Whit Sheard of Pacific Environment.

The lawsuit said a rapid increase in industrial activities since 1993 has been accompanied by more frequent polar bear incidents.

Between 1994 and 2000, oil and gas operations reported 258 polar bear sightings, an average of just over 37 per year, and 66 instances of direct harassment of polar bears, an average of fewer than 10 per year, the lawsuit claims.

But in 2004 alone, it says, oil and gas operations reported 89 sightings and 36 instances of direct harassment of polar bears.

The agency presumes without study that the industry will continue to have a negligible effect on the bear and walrus population, Siegel said.

"There should have been a really meaningful, rigorous, hard look at the cumulative impacts," she said.

The lawsuit asks the federal court to declare the Fish and Wildlife Service regulations illegal and force the agency to do a thorough analysis of how global warming and oil exploration and development affect polar bears and walrus.

Earthjustice attorney Jernigan said the groups are not asking that any specific petroleum operation be halted if the lawsuit is successful. Instead, he is hopeful that it will require oil and gas companies to have to seek authorization yearly for site-specific operations.